The impact tool comprises an impact mechanism provided within a housing. The impact mechanism includes a piston for causing an impactor to move in accordance with its motion, thereby directly or indirectly striking a bit installed at an end of the housing. The reciprocating motion of the impactor is obtained by converting a rotation of a motor-driven crank shaft into a reciprocating motion of the piston by means of a crank mechanism in which an eccentric pin provided on the crank shaft is connected to the piston by a connecting rod.
Optionally, the impact tool may also comprise a vibration damping mechanism provided to reduce vibration generated by a striking operation of the impact tool. This vibration damping mechanism typically has a well-known configuration, for example, as illustrated in Patent Document 1, such that a rotary plate is mounted on the eccentric pin of the crank shaft, a second pin is provided protrusively on an upper side of the rotary plate in a position point-symmetric to the eccentric pin, and a counterweight is connected via a rod or the like to the second pin. That is, the shift in the center of gravity, derived from the reciprocating motion of the piston, is canceled out by the reversely moving counterweight, so that the vibration can be reduced.
Patent Document 1: Japanese Laid-Open Utility Model Application, Publication No. 51-6583